It is a triumph of marketing over evidence that millions take supplements every day. There is no question we need vitamins in our diet to live. But do we need vitamin supplements? It’s not so clear. There is evidence that our diets, even in developed countries, can be deficient in some micronutrients. But there’s also a lack of evidence to demonstrate that routine supplementation is beneficial. And there’s no convincing evidence that supplementing vitamins in the absence of deficiency is beneficial. Studies of supplements suggest that most vitamins are useless at best and harmful at worst. Yet the sales of vitamins seem completely immune to negative publicity. One negative clinical trial can kill a drug, but vitamins retain an aura of wellness, even as the evidence accumulates that they may not offer any meaningful health benefits. So why do so many buy supplements? As I’ve said before, vitamins are magic. Or more accurately, we believe this to be the case.

There can be many reasons for taking vitamins but one of the most popular I hear is “insurance” which is effectively primary prevention – taking a supplement in the absence of a confirmed deficiency or medical need with the belief we’re better off for taking it. A survey backs this up – 48% reported “to improve overall health” as the primary reason for taking vitamins. Yes, there is some vitamin and supplement use that is appropriate and science-based: Vitamin D deficiencies can occur, particularly in northern climates. Folic acid supplements during pregnancy can reduce the risk of neural tube defects. Vitamin B12 supplementation is often justified in the elderly. But what about in the absence of any clear medical need?

The question many have is a straightforward one: Is taking a multivitamin going to do more harm than good? To answer this, we should look at all the evidence in a systematic way, evaluate risks and benefits, estimate the overall odds of a good outcome, and then make a decision that would weigh these factors against considerations like cost. Happily, an updated analysis summarizes the evidence for vitamins to treat two of the biggest killers: cardiovascular disease, and cancer.

Some of these were huge trials with long durations, which should have been able to detect a difference if any existed. And some studies detected small differences in some groups. But overall, multivitamins were found to have no effect on cardiovascular disease or cancer risk. If multivitamins are beneficial, the effect is too small to detect. Reassuringly, there was no consistent pattern of harms, though subgroup analysis and some individual studies identified elevated cancer or cardiovascular risks.

With individual and paired supplements, there was a lack of good evidence for several vitamins. Overall, there was no strong evidence of either a beneficial or detrimental effect with vitamins A, C, or D, folic acid, selenium, or calcium. The evidence for beta-carotene was more clear: it had no effect on cardiovascular disease, cancer, and mortality. In high-risk subgroups, beta-carotene was associated with an increased cancer risk. The evidence for vitamin E was also clear – it has no beneficial effects.

I’ve blogged about the risks and benefits of calcium and vitamin D before so I was interested in the findings with this combination. Calcium, with or without vitamin D, seems to have no meaningful effects on cancer or cardiovascular disease. However, there was also no clear evidence of harms, either.

The authors point out in their discussion that their review isn’t the first to identify a lack of benefit from vitamin supplements, there are at least ten others that have drawn similar conclusions. They also point out the challenge of studies of this kind – you need thousands of participants and must follow participants for several years, which makes for a very costly trial. However, given the continued interest (and spending) on multivitamins, this might be a worthwhile investment. But given the perennial popularity of multivitamins, would a negative trial actually make a difference?

The thing to do with [these reports] is just ride them out…we see no impact on our business.

- Joseph Fortunato, Chief Executive of General Nutrition Centers, quoted in Do You Believe in Magic? by Paul Offit

The USPSTF’s recommendations

The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of the use of multivitamins for the prevention of cardiovascular disease or cancer.

The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of the use of single- or paired-nutrient supplements (with the exception of beta-carotene and vitamin E) for the prevention of cardiovascular disease or cancer.

So there is insufficient evidence to establish a clear benefit or harm. Both recommendations are given an “I” rating which means that if the product is offered/suggested, patients should understand the uncertainty about risk and benefit.

Beta-carotene and vitamin E get their own recommendation:

The USPSTF recommends against the use of beta-carotene or vitamin E supplements for the prevention of cardiovascular disease or cancer.

This is a “D” recommendation, which means use should be discouraged.

Conclusion

Without demonstrated benefit, there’s currently no clear rationale to justify multivitamin supplements or individual vitamins to prevent cardiovascular disease or cancer. Taking vitamins for “insurance” doesn’t appear to be harmful, but the evidence isn’t conclusive. It’s concerning that the two individual supplements for which we do have good evidence also have the least attractive risk/benefit profiles. While the risk of harms do seem low, (especially if you avoid vitamin E and beta-carotene), there’s also no evidence supplementation offers any upside. I’m a believer in the hypothesis that supplement consumption may actually worsen dietary intake, so my advice remains unchanged: If you believe your diet is unhealthy or insufficient to meet your nutritional requirements, then change your diet instead of adding supplements. Supplements should be reserved for when there’s an actual dietary deficiency or medical need that cannot be met through diet. You won’t see this message advertised anytime soon by the supplement industry.

44 thoughts on “Do vitamins prevent cancer and heart disease?”

“Calcium, with or without vitamin D, seems to have no meaningful effects on cancer or cardiovascular disease. ”

Scott, what about supplemental Ca for osteoporosis in post-menopausal women and prophylactic Ca for younger women? Calcium is being added to a variety of foods and beverages but the purported benefit was apparently not studied for this report. Any value for that population?

Scott, thanks for an excellent summary of this topic. Much of the confusion on this topic arises because the public does not understand what a requirement is, and how that requirement is set. The public hears a particular requirement and assumes that, if they do not consume this intake every day, then their health is at risk. This is completely untrue. Requirements are set, in part, through statistical procedures and the public has little grasp of statistics and what they mean.

This can be coupled with the typical philosophy that, if some is good, then more is better. I think the epidemiology studies have not helped this, in that breaking groups into quartiles or quintiles can give an unintentional misleading impression that the response curve is linear or plateaus rather than an inverted-U shape.

I am going to stick my neck out and offer that, if the SBM owners are interested, they could contact me off-list and I would be happy to write a post that describes what we really mean by a requirement, how we set them, and why intakes above that are unnecessary for a vast majority of the population. From what I’ve read in this fine blog over the years, this is an information gap that the readers may find useful.

I would also be interested in reading this post Angora Rabbit. Is there a reason you don’t currently write for SBM? You often have many useful and interesting things to add to the conversation, and I couldn’t count how many times I’ve seen someone comment “I hope Angora Rabbit can elaborate/clarify this issue”.

I wasn’t fishing, but thanks for the kind words. I’m a full-time tenured professor at a tier-one institution and my plate is sadly* fairly full between running a research lab with grad students and postdocs, teaching our large pool of undergrad majors, and doing the administrivia stuff. I had the pleasure of being on sabbatical last year and it was truly like Christmas every day.

I would love to blog more! Sadly, when I post it is usually because I have snatched a moment when there isn’t a fire to put out or all the airplanes have finally landed safely. I honestly don’t know how full-time academicians like Drs. Gorski, Novella, etc. make the time to write on a weekly basis. My bunny ears are tipped in admiration!

I would also like to see a post on these topics. In particular I have a friend who is an Advocare distributor who has made comments about RDA levels haven’t been changed for some time and are old and that they are “minimums” rather than maximums.

Same question as windriven.
———
Vitamin-taking is often the gateway drug to all kinds of woo. You start with a multi for “insurance” and ignore your doctor when s(he) says you don’t need them if you eat a decent diet, because everyone just knows that “doctors know nothing about nutrition” (and the person who just said this is presumed to know everything about it, of course).

Then you hear or read that Vit C helps colds, that you need calcium for your bones, so you add those. Then you pick up some book by an MD (!) that says the soil is all depleted and our food is devoid of most essential nutrients, so you get B Vitamins and trace mineral supplements.

Next up, you go for some acupuncture because most of the stuff you read, including some respected newspapers (and 90 percent of anything you Google) says it works! The nice, caring practitioner lets you know that ancient Chinese medicine has been helping people like you for thousands of years with simple herbs that can’t be patented and make fortunes for greedy pharma shills.

Calcium alone won’t make a difference for oesteoporosis because it needs other cofactors such as Vitamin D, Vitamin K and excercise. Calcium-rich foods like dairy are not the answer, either. World-wide, cultures that have the highest calcium dietary intake also have the highest rates of oesteoporosis. Many cultures with extremely low calcium intake have no oesteoporosis.

This is another meaningless study, very very poorly designed, conducted by people who have no clue.

(full disclosure) I do take a daily multi-vitamin
I also exercise 4-5 days a week with high intensity for at least an hour.

The studies here are “General population”. My question is, should I supplement with this level of physical activity, or is it a waste of time/money?

as an aside, I take iron supplements (esp right before I give blood) since my hemoglobin/hematocrit tests borderline/low. My doctor believes its a “sports anemia” situation (increased plasma volume due to exercise vs actual low iron)

I wrote specifically about antioxidant supplements and exercise in the past and the evidence seems to be leaning towards harmful. The most cautious approach suggests striving to meet nutritional requirements through food alone. Any increased demands can be met through increased caloric intake. I’ve also blogged about iron supplements and exercise. In some cases iron supplements are warranted.

What about electrolyte replacement? At what level/duration of intensity/sweatiness would that be a good idea? I myself swim for exercise, and it’s not overly intense, and I’m too cold to sweat, but occasionally I cramp up in the toes, at which point I am forced to end my session. I wonder if taking an electrolyte supplement might prevent this? I don’t regularly take any supplements, though, aside from the odd vitamin D because I’m always indoors and I wear sunscreen every day.

If I may be so bold, I think the “electrolyte replacement” gambit is overblown. I play an hour of ice hockey every Thursday morning and when I step off the ice, I am literally soaked in sweat. Whether I drink coconut water, gatorade or regular water I don’t notice a bit of difference in my recovery. As a matter of fact I don’t notice anything at all, other than my legs being a bit sore.

Sorry forgot to add, the cramping is likely a result of poor circulation to your feet caused by chronically tight calf muscles, which is typical of many people. Stretching cold muscles can lead to injury, so I suggest you try doing some static calf stretches after a few minutes of swimming. Alternatively you could warm them by jogging on the spot for a couple of minutes then doing the stretches before you begin swimming. I hope this helps.

“If you believe your diet is unhealthy or insufficient to meet your nutritional requirements, then change your diet instead of adding supplements.”
Maybe it’s been said better than that before, but I’ve not read it.

I struggle to find time to cook great things but I do pretty well, partly cause good food feels very rewarding to me – I grow, gather, and kill things (this Sat= slaughtering giant turkeys). I do notice that now days, many people are unable to find the time. Meetings at 6 PM are not uncommon – you are expected to grab something quick at some store, and it’s not considered a problem by most people. Nothing new here, just one of Pollan’s laments.

It’s not so much finding the time as prior proper planning. I have a bunch of fun food allergies (thankfully, none life-threatening, just unpleasant) and grabbing quick food isn’t an option unless it’s a salad from Subway.

I can still make it with limited time during the day, I just have to actually plan out every time I eat for the day before I leave my apartment. (And there are plenty of healthy grab and go snacks out there!)

I’m male, 72 and have been taking 2 Citracal tablets daily for some time. My wife is Asian and about age 50 started showing lactose intolerance. She stated Ca supplementation and switched to soy milk. (Her job at the time was a med tech measuring bone density.)

After reading about possible problem with excess Ca I am backing off to 1 Citracal tablet daily. I tend to drink a gallon of milk in about a week. That and other Ca sources puts me at ~1000mg daily.

My change is unlikely to have any negative health impacts. But it will make a small positive financial impact.

I agree most supplements are useless or harmful. Having said that, this only applies to nutritionally replete individuals. In my practice, I see multiple people with vitamin deficiencies who are of high social class. A lot of people eat only junk food, even the elderly. The commonest vitamin deficiencies appear to be B12 and vitamin D; and in the elderly and in premenopausal women, iron deficiency (a mineral, not a vitamin) is very common. Conversely, I cannot remember the last time I saw a folate deficiency – thanks to fortification of the grain supply in this country.

I take 4 specific supplements because I’m a vegetarian. There is evidence that vegetarians who do not supplement have significant deficiencies of vitamin D, B12, DHA and iodine. I get the rest of the panoply of vitamins, minerals and assorted micronutrients from my diet. This is preferable in every respect to getting vitamins from pills, and I would certainly eliminate my supplements if I could.

Just a couple of comments. The issue with this post is that the term “vitamins” refers to a diverse collection of different molecules, and this post also seems to lump minerals in with them. They all have different biological effects. I agree that people should not take a multivitamin supplement as insurance against cancer or heart disease (although the Physician’s Health Study indicated that there was a modest reduction in cancer with long term use (http://www.ncbi.nlm.nih.gov/pubmed/23162860)), however there are pockets of the population that are vitamin deficient and a supplement could be seen as nutritional insurance to avoid deficiency.

Using dietary supplements does not in fact make people more inclined to poor dietary habits. Dietary supplement use appears to be a marker for better health and diet. That is, people who take dietary supplements are more likely to have an adequate diet (without including the additional nutrients from supplements) than people who do not take them. This is a theme that shows up in many studies that look at nutrient inadequacy. http://www.ncbi.nlm.nih.gov/pubmed/17659898 and http://www.ncbi.nlm.nih.gov/pubmed/17209210 are the first hits that I got on pubmed but the association is fairly robust.

The RDA is in fact the minimum level needed to achieve sufficiency in 98% of the population. The idea is to get your intake between the RDA and the UL (tolerable upper intake level). The UL is the lowest level of chronic intake that is not associated with adverse effects. Some of the ULs are important not to exceed, e.g. vitamin A. For others, the choice of the level seems to be based on unexpected criteria such as possible gastrointestinal discomfort for vitamin C as the intestinal microflora can use the large amount of ascorbic acid that remains undigested in the stool as a source of energy. Some vitamins do not have a UL. The UL is different to acute toxicity.

Both of these trials reported cancer outcomes, and while the smaller trial found a statistically significant decrease in overall cancer incidence over 4 years (43), the larger trial did not (44). The pooled unadjusted relative risk was 0.98 (95% CI, 0.91 to 1.04).

Really? After this pair of sentences pooling together 1100IU/day and 400IU/day (little more than a third of the former) as if they were the same I have to admit that I don’t care what Dr. Fortmann et alter conclude here or elsewhere.

Two years after randomization, a comparison of serum 25-hydroxyvitamin D levels in 227 women in the group given calcium with vitamin D and 221 women in the placebo group revealed that the levels were 28 percent higher in the supplement group.

Regarding vitamin E. I have no interest on results of any intervention trial with dl-α-tocopherol since 7/8 of it are xenobiotic substances that I don’t consider vitamin E (some of them inferior analogs at most). They should have been isolated and its safety verified. From Jensen & Lauridsen (2007):

Synthetic all-rac-alpha-tocopherol consists of a racemic mixture of all eight possible stereoisomers. Assessing the correct biological activity in form of bioavailability and biopotency has been a great challenge during many years as it is difficult to measure clinical endpoints in larger animals than rats and poultry.<<<…>>> For humans and other animals, only different biomarkers or surrogate markers of bioactivity have been measured, and due to the lack of good biological markers for bioactivities, bioavailability is often used as one of the surrogate markers for bioactivities with those limitations this must give.

So I disregard references 20, 31 and 33. That leaves us with two studies.

Results. The average increase of the mean IMT was 0.020 mm year-1 amongst men randomized to placebo and 0.018 mm year-1 in vitamin E, in vitamin C and 0.017 mm year-1 0.011 mm year-1
in the vitamin combination group (P = 0.008 for E + C vs. placebo). The
respective means in women were 0.016, 0.015, 0.017 and 0.016 mm year-1.
The proportion of men with progression was reduced by 74% (95% CI
36±89%, P = 0.003) by supplementation with the formulation containing
both vitamins, as compared with placebo.

Since I am a man I will keep supplementing both. My choice.

Nevertheless I first and foremost focus on a high quality diet, no ironic effect around here.

Because we get less sun than most of our ancestors, Vitamin D is one of the few nutrients for which substantial numbers of otherwise healthy, decently fed people in the USA don’t get enough.

However, it’s fat-soluble, which means you can get too much in a hurry. I wouldn’t go supplementing above the RDA unless you’re being treated for low blood levels, with follow-up blood tests to make sure that it’s working and you don’t go into excess.

High dose intravenous vitamin C for viral infections still awaits a refutation though.

You really shoot yourself in the foot on the somewhat sensible vitamin D stuff when you overhype the benefits of vitamin C. There have been lots of small trials with various methods of vitamin C supplementation that come out positive, but they are usually too small or involve tedious methodology to merit clinical significance. The large scale trials come out negative. I’m having trouble finding a single SBM post about this topic but I know it’s been covered before by both Scott Gavura and Mark Crislip.

Saying things over and over again doesn’t magically turn them into truth. Stop doing it.

I wouldn’t go supplementing above the RDA unless you’re being treated for low blood levels, with follow-up blood tests to make sure that it’s working and you don’t go into excess.

@Young CC Prof: Actually I didn’t measure levels before going to 5000IU/day the days I didn’t sunbath at midday. I didn’t go up to 5000IU/day until I read about magnesium and vitamin K2. I did measure 25-OH-vitamin-D twice a year last two years and it has been at the 50-60ng/dl range (except the first time, 45ng/ml) that is where I have decided it to be following Vitamin D Council advice.

@Sawyer.

You really shoot yourself in the foot on the somewhat sensible vitamin D stuff when you overhype the benefits of vitamin C.

There have been lots of small trials with various methods of vitamin C supplementation that come out positive, but they are usually too small or involve tedious methodology to merit clinical significance. The large scale trials come out negative. I’m having trouble finding a single SBM post about this topic but I know it’s been covered before by both Scott Gavura and Mark Crislip.

Saying things over and over again doesn’t magically turn them into truth. Stop doing it.

Sorry to disturb you but you have to prove me wrong in what I say. I say precisely that the hypothesis “high doses (lets say 0.4g/kg per day) of intravenous/intramuscular vitamin C has a powerful viricidal effect” has not being falsified à la Popper. Proof me wrong and point me toward where it has been refuted. All I have found is supporting evidence from the original clinical experience by late Dr. Klenner forward.

@medsvstherapy.

Regarding vitamins and supplements: we see the same story lines as with other profitable but unproven ideas: one is “you did not have a high enough dose,” and another is “you did not use the correct preparation.”

Well, that’s kind of the point. When people hear about vitamin C supplementation, they assume it means a once a day vitamin that they pop into their mouth and then forget about. They don’t realize that the research that shows efficacy has protocols that no person in their right mind is going to waste their time on (unless they are vitamin deficient).

The first paper I found when researching this topic was one that promised a clear correlation between vitamin C and reduced cold symptoms. Awesome! The treatment protocol? HOURLY supplements in a hospital for SIX HOURS followed by a reduced dosage. That’s the level of care needed to get clinically significant effects, assuming they are real effects and not just an artifact of a poorly structured experiment. How many people that promote the use of vitamin C have any clue what’s required to see an actual benefit?

Despite their emphasis on hard science, the people on this site are interested on how medicine works in the real world. Vitamin C doesn’t clear the bar as a sensible treatment of common viral infections, let alone cancer or heart disease (which is what this post was actually about before you steered off-topic).

Regarding vitamins and supplements: we see the same story lines as with other profitable but unproven ideas: one is “you did not have a high enough dose,” and another is “you did not use the correct preparation.”

The vitamin C people have continued to be enthusiastic with the ‘not a high enough dose’ for decades.

“Micronutrients” The Woo-meisters keep using that word but I do not think it means what they think it does. I have yet to see anyone with molybdenum, germanium, tin or cobalt deficiency, nor a coherent description of the symptom constellation that accompanies such deficiency. Yet the Nu-Skin people have made millions pushing their supplements.

I’m living proof a balanced, nutritious diet will contribute to exceptional levels of anti-oxidants in my skin according to their Biophotonic scanners. Whether that translates into better health remains to be seen.

OK, Jeff – this is a silly game. Let’s get scientific. What do you think vitamin C cures? Or ameliorates?
And what is the dose, schedule, and administration route preferred by the true believers?
Then, we can progress to seeking affirmative data, rather than you making my point for me by posting an example of what I said always gets thrown out there: “the dose was not high enough.”

I see this:
Maggini 2012: “A combination of high-dose vitamin C plus zinc for the common cold.”
Wow. At day 5, 30% of placebo and 50% of vitaC plus zinc no longer with runny nose, one of eight monitored symptoms.

As much as all the vitamin research annoys me, it is a fantastic teaching tool for how to read and interpret medical literature. The mistakes that the vitamin fanboys make are very similar to the mistakes mainstream medical researchers can make: overly elaborate procedures needed for positive results, inconsistent standards for dosage, too much focus on non-specific effects, throwing results from abstracts together rather than systematically looking at the raw data, confusing statistical significance for clinical significance, etc.

I’m am somewhat grateful to these guys for helping me learn so much about bad research techniques without ever having to step into a laboratory.

http://online.wsj.com/news/articles/SB10001424127887324338604578326160736614012
“At the end of the study, 3.8% of the Mediterranean-diet-plus-olive-oil and 3.4% of the Mediterranean-diet-plus-nuts groups suffered a heart attack, stroke or death from cardiovascular disease. By comparison, 4.4% of members in the control group suffered this outcome. The differences in the risk of stroke were statistically significant. The differences in the risk of heart attack weren’t, possibly because of the low incidence of heart attacks among people in the study, researchers said.”

What’s your take on fortified breakfast cereals, fortified low-fat milk, enriched bleached flour, and iodized salt, which basically had vitamin and mineral supplements added to them, just not in pill form.

I know you are not asking me, Max, but my take on them is that they prevent anemia in children, rickets, neural tube defects and hypothyroidism, respectively.

Thus I am not against per se the wholesale fortification of the food supply with minerals or vitamins at source.

Though we do have to deal with the laws of unintended consequences, such as the rapid increase in colorectal cancer that we saw once flour fortification with folic acid became mandatory – likely due to the fact that FA is a cancer promoter.

In general, these fortification policies really deal with people on marginal diets, though there may be benefits across the general population too (such as in the case of iodination of salt and flouridation of water). As a vegetarian, I am hyper-aware of which foods and vitamins I need to eat, but I doubt my case is typical of 98% of the eating public who are omnivores.

In order to make any sweeping statements either for or against the efficacy of a drug or a vitamin / mineral in a particular disease you need to take into account the mechanisms via which the substance may have an effect.

To say there’s no evidence that vitamin (and presumably you subsumed minerals and EFAs under the term “vitamins”) supplementation is a good preventative against disease, incl. cancer, is ignorant.

Consumer should, however, watch out for ingredients incl excipients in supplements available in the retail environment – most of which are manufactured by the pharmaceuticals industry. Better to seek out a naturopath who will prescribe ‘practitioner only’ products which have been approved by the relevant medicine approval body in your country.

Though taking supplements is not intended to replace eating a healthy, largely unprocessed diet, it has long been known that today’s crops do not yield the high vitamin and, particularly, mineral content, nor the higher protein to carbohydrate ratios of the past. Combine this with the modern stressors to our health, such as chronic stress (which itself depletes the body of various vitamins and minerals), the consumption of highly processed foods and non-drinks / non-foods, and the consumption of both social and prescription drugs which further deplete the body of nutrients, it’s a no-brainer that taking supplements is beneficial.

Of vitamin supplementation, NBC specifically said that a “very extensive look at the studies that have been done show it may be a waste of time when it comes to preventing the diseases most likely to kill you.”

The “very extensive look” encompassed 24 preselected studies. It looks like they just possibly may have missed a few, such as these:

Vitamins C and E, as well as other nutrients were shown to reduce all-cause, cancer and CVD mortality risks in a long-term study of 16,000 adults,
The study showed that mortality risks were inversely associated with blood levels of these antioxidants.
For instance, the group with the highest blood concentrations of vitamin C were 45 percent less likely to die of any cause; the highest vitamin C levels were shown a 60 percent reduced risk of dying from cancer.http://www.ncbi.nlm.nih.gov/pubmed/?term=serum+antioxidant+nutrients%2C+vitamin+a%2C+and+mortality+in+us+adults

Immunity:
“Supplementation of vitamin C improves the function of the human immune system, such as antimicrobial and natural killer cell activities, lymphocyte proliferation, chemotaxis and delayed-type hypersensitivity. Vitamin C depletion has been correlated with histaminemia which has been shown to damage endothelial-dependent vasodilation.”http://www.ncbi.nlm.nih.gov/pubmed/23830380

Vitamin C deficiency may be a key driver of the now ubiquitous arthitic symptoms pandemic around the world and can be reversed using vitamin C supplements, as this case shows:

I have seen the results of beri-beri. It was in former POWs captured by the Japanese in WW2 who nearly starved to death. We never see it in people eating a regular diet. And I’ve read about scurvy in sailor who ate only hardtack and salted pork for months at a time who got no vitamin C. Again, not seen much in people with access to a varied diet.

On folic acid; supplementation has to be initiated BEFORE conception in order to decrease NTD risk. By the time you discover you’re pregnant, the critical period of neural development has already passed.

There are major problems in discussing the whole area of nutrition and that is that almost all of the research is rubbish, and this rubbish is used or miss-used by both quacks, governments and medics. Most of the research has been produced by credible sources and is based on epidemiology, often with very unreliable data collection & is largely meaningless. When we read official recommendations about diet etc it is no more reliable than what quacks use. The main problems occur when idiots use these “natural” supplements in doses that are far from natural, in the belief that because they are natural they are safe. These things go in and out of fashion faster than the weather changes, fashion usually supported by the latest research. Fish oils have been marvelous or useless every other week for years. If you have an opinion it will be wrong shortly. I just keep my head down.